Explanation:

- CBSE refers to the Central Board of Secondary Education, which conducts exams for students in India.

- When students miss exams, an alternative method is needed to assign their marks.

- The term "formula" is typically used to describe a systematic method or rule for calculation.

1. Formulae: This is the plural form of "formula." It would be used if multiple sets of rules or methods were involved.

2. ?Equation: This is a mathematical statement asserting the equality of two expressions. It is not used in the context of devising a system for marking.

3. Formula: The singular "formula" is appropriate here. It refers to a specific method or rule used to calculate marks.

4. Formation: This refers to the action of forming or creating something. It is irrelevant in this context.